I am currently building a solid mounted four speed gearbox engine. I have two front engine covers available[nose piece]. One has a overall length of 6 5/8 inch, the other 7 3/8 inch. The short one is the same length as the one fitted to my RL engine, that uses the nut to secure the starting handle shaft. The Source Book tells me; that RM and RN three speed gearbox engines changed to a pin type starting handle shaft. Am I correct in assuming the short cove is for the three speed gearbox engines? Both the Source Book and Wyatt state the crankcase changed for the four speed geabox, but there is no mention of changes to the front cover.

Location: s.wales

The short shaft has a dog engagement with the crankshaft while the longer one uses the pin with sort of hook arrangement on the crank.
The dog type shaft has a nut in the front of the nosepiece on which the shaft runs. The later one has a sleeve on the handle that runs in the nosepiece.
The old Austin Seven Centre parts list illustrates both types and also lists the dog engagement as being for coil engines, with the pin type engagement as 1930-36.
Very likely the change happened about the time of the short scuttle body appearing, which ties in with RM & RN. RL probably short nosepiece.

Location: Melrose, Scottish Borders

Hello John,
I found this article good for explaining the difference and reasons.
http://www.austin7.org/Technical%20Articles/Nose%20Cones/
Hopefully it makes your choice a bit easier.

Location: United Kingdom

Thank you Timothy, fully explained. My assumption was wrong regarding which length for which engine.

Location: s.wales

Also, our thanks to Sandy...